body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #e8f4f8;
    margin: 0;
    padding: 20px;
    min-height: 100vh;
}

.container {
    max-width: 600px;
    margin: 0 auto;
    background-color: white;
    padding: 30px;
    border-radius: 12px;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
}

h1 {
    text-align: center;
    color: #333;
}

.difficulty-select {
    text-align: center;
    margin: 20px 0;
}

.difficulty-btn {
    padding: 12px 24px;
    margin: 0 12px;
    background-color: #4CAF50;
    color: white;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    font-size: 16px;
    transition: all 0.3s ease;
}

.difficulty-btn:hover {
    background-color: #45a049;
}

.game-container {
    margin-top: 20px;
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 1px;
    background-color: #333;
    border: 2px solid #333;
}

.cell {
    aspect-ratio: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: white;
    font-size: 20px;
    cursor: pointer;
}

.cell.fixed {
    background-color: #f0f0f0;
    font-weight: bold;
}

.cell.selected {
    background-color: #7ea8c1;
    box-shadow: inset 0 0 8px rgba(0, 0, 0, 0.3);
}

.cell.error {
    background-color: #ffcccc;
}

.restart-btn {
    display: block;
    margin: 20px auto;
    padding: 10px 20px;
    background-color: #f44336;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 16px;
}

.restart-btn:hover {
    background-color: #d32f2f;
}

.hidden {
    display: none !important;
}

.hearts-container {
    display: flex;
    gap: 8px;
    margin-bottom: 10px;
}

.heart {
    color: red;
    font-size: 24px;
}

.heart.white {
    color: #ccc;
}

.cell.highlight-row,
.cell.highlight-col,
.cell.highlight-box,
.cell.highlight-number, .number-count.highlight-number{
    background-color: #e6f7ff;
}
.success-modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.success-content {
    background-color: white;
    padding: 30px;
    border-radius: 10px;
    text-align: center;
    max-width: 400px;
    width: 80%;
}

.success-title {
    font-size: 24px;
    margin-bottom: 20px;
    color: #4CAF50;
}

.success-buttons {
    display: flex;
    justify-content: center;
    gap: 20px;
    margin-top: 20px;
}

.success-btn {
    padding: 10px 20px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 16px;
    transition: all 0.3s ease;
}

.success-btn.continue {
    background-color: #4CAF50;
    color: white;
}

.success-btn.exit {
    background-color: #f44336;
    color: white;
}

.success-btn:hover {
    opacity: 0.9;
}

.number-counts-container {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 12px;
    margin: 20px 0;
    padding: 15px;
    background-color: #f8f9fa;
    border-radius: 10px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.number-count {
    font-size: 24px;
    color: #333;
    padding: 8px 12px;
    background-color: white;
    border-radius: 6px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
    min-width: 40px;
    text-align: center;
}

.number-count sup {
    font-size: 14px;
    color: #666;
    margin-left: 2px;
}